Process for preparing C3-6 (hydro)fluoroalkenes by dehydrohalogenating C3-6 halo(hydro)fluoroalkanes in the presence of a zinc/chromia catalyst

Abstract

The invention relates to a process for preparing a C3-6 (hydro)fluoroalkene comprising dehydrohalogenating a C3-6 hydro(halo)fluoroalkane in the presence of a zinc/chromia catalyst, wherein the C 3-6 (hydro)fluoroalkene produced is isomerised in the presence of the zinc/chromia catalyst.

We claim: 
     
       1. A process for preparing a C 3-6  (hydro)fluoroalkene comprising dehydrohalogenating a C 3-6  hydro(halo)fluoroalkane in the presence of a zinc/chromia catalyst, wherein the C 3-6  (hydro)fluoroalkene produced is isomerised in the presence of the zinc/chromia catalyst. 
     
     
       2. A process according to  claim 1  wherein. the C 3-6  (hydro)fluoroalkene exists in E and Z isomers, and the ratio of E and Z isomers is changed in the presence of the zinc/chromia catalyst. 
     
     
       3. A process according to  claim 2  wherein the presence of the zinc/chromia catalyst changes the ratio of E and Z isomers from that which is the kinematic determined mixture of isomers from the preparation of the C 3-6  (hydro)fluoroalkene. 
     
     
       4. A process according to  claim 2  wherein a desired isomer of the C 3-6  (hydro)fluoroalkene is recovered in a subsequent step. 
     
     
       5. A process according to  claim 1  carried out at a temperature of from −70 to 400 °C. and a pressure of from 0 to 30 bara. 
     
     
       6. A process according to  claim 1  for preparing a (hydro)fluoropropene comprising dehydrohalogenating a hydro(halo)fluoropropane. 
     
     
       7. A process according to  claim 6  wherein the (hydro)fluoropropene produced is selected from tetrafluoropropenes and pentafluoropropenes. 
     
     
       8. A process according  claim 7  for preparing 1,2,3,3,3-pentaftuoropropene (CF 3 CF═CHF). 
     
     
       9. A process according to  claim 7  for preparing 1,3,3,3-tetrafluoropropene (CF 3 CH═CHF). 
     
     
       10. A process according to  claim 7  for preparing 2,3,3,3-tetrafluoropropene (CF 3 CF═CH 2 ) and 1,2,3,3,3-pentafluoropropene (CF 3 CF═CHF). 
     
     
       11. A process according to  claim 7  for preparing 2,3,3,3-tetraftuoropropene (CF 3 CF═CH 2 ) and 1,3,3,3-tetrafluoropropene (CF 3 CH ═CHF). 
     
     
       12. A process according to  claim 1  wherein the dehydrohalogenating step is carried out in the presence of a feed comprising hydrogen fluoride (HF). 
     
     
       13. A process according to  claim 1  wherein the dehydrohalogenating step is carried out in the absence of added hydrogen fluoride. 
     
     
       14. A process according to  claim 1  wherein the zinc chromia catalyst comprises 0.01 % to 25% by weight zinc. 
     
     
       15. A process according to  claim 1  wherein the zinc chromia catalyst is amorphous or from 0,1 to 50% by weight of the catalyst is in the form of one or more crystalline compounds of chromium and/ or more crystalline compounds of zinc. 
     
     
       16. A process according to  claim 5  wherein the process is carried out in the vapour phase at a temperature of from 200 to 360° C. 
     
     
       17. A process according to  claim 5  wherein the process is carried out at super-atmospheric pressure. 
     
     
       18. A process according to  claim 1  wherein the process is carried out with a diluent gas. 
     
     
       19. A process according to  claim 18  wherein the diluent gas comprises nitrogen. 
     
     
       20. A process according to  claim 18  wherein the diluent gas comprises the resultant C 3-6  (hydro) fluoroalkene or an isomer rich blend of the C 3-6  hydro)fluoroalkene. 
     
     
       21. A process according to  claim 1  wherein the process is carried out in the presence of HF and at atmospheric or sub-atmospheric pressure and wherein the ratio of HF to hydro(halo)fluoroalkane is greater than 1.5:1.